Etching composition and method of etching



3,296,142 ETCHING COMPOSITION AND METHOD OF ETCHING Abraham IsidorSherer, Clifton, NJ., and John Ruzlcka,

Brooklyn, N.Y., assignors to Ball Brothers Company Inc., Muncie, Ind., acorporation of Indiana N Drawing. Filed Apr. 6, 1964, Ser. No. 372,053

14 Claims. (Cl. 252-794) This application is a continuation-in-part ofapplication Serial No. 80,993, filed January 6, 1961, which in turn is acontinuation-in-part of application Serial No. 688,826, filed October 8,1957, now abandoned.

This invention relates to a novel etching composition and method andmore particularly relates to a new and improved etching composition foruse in the powderless etching of printing plates and relates to a novelmethod of powderless etching using such composition.

Various types of powderless etching compositions have been proposed inthe past but none of the compositions previously suggested have provento be completely successful. For example, Patent No. 2,828,194 disclosesan etching composition in which a sulfated castor oil is employed incombination with nitric acid and an organic liquid. This etching bathdid not produce the degree of etching quality required by the printingindustry, and in addition, was inconsistent, unpredictable anduncontrolled in its etching performance.

Patent No. 2,979,387 discloses an etching composition containing analkyl aryl sulfonate in combination with nitric acid and an organicliquid. Plates etched with this composition also were not consideredcompletely 'successful because of insufiicient depth of etch between theimage surface and the recessed portions of the plate. Furthermore, ifthe proportion of the alkyl aryl sulfonate was changed in an attempt toachieve greater depth, undercutting of the image area resulted. Thus,alkyl aryl sulfonate etching compositions were also not commerciallysuccessful.

In view of the above and other deficiencies and shortcomings of etchingcompositions heretofore employed, it was completely unexpected andsurprising to discover the new and improved etching composition andetching method of the present invention. The smoothness of the shoulderand the speed of etching are substantially improved. Also, the etchedimage produced is not undercut but has an acceptable shoulder angle.Furthermore, the etching composition of the invention provides greaterflexibility in the formulation of the etching bath.

The etching composition of the present invention comprises a sulfatedcastor oil, an alkyl aryl sulfonate, a petroleum solvent and water.Prior to etching, the above composition is mixed with nitric acid andadditional water to form the etching bath.

The sulfated castor oil employed in the etching composition of theinvention advantageously has on a dry basis between about 6% and 9% byweight of organically combined S0 an acid value of between about 18% and25% by weight calculated as oleic acid, and an alkalinity of betweenabout 2.2% and 3% calculated as KOH.

The alkyl aryl sulfonate advantageously has an alkyl group with betweenabout 10 and .12 carbon atoms. Particularly useful for use in theetching composition of the present invention are alkyl benzenesulfonates, such as sodium dodecyl benzene sulfonate, sodium decylbenzene sulfonate, dodecyl benzene sulfonic acid, etc.

The petroleum solvent is advantageously an aromatic solvent, forexample, Solvesso 150 sold by Esso Standard Oil Co., Modsol 52 sold byAmerican Mineral Spirits Co., etc.

The proportion of the sulfated castor oil in the etching United StatesPatent 0 ice composition is advantageously between about 25 and 40% byweight and preferably between about 30% and 35%. The alkyl arylsulfonate is advantageously present in a percentage between about 0.3%and 2% by weight and preferably between about 0.9% and 1.2%. Theproportion of solvent is preferably between about 60% and 72% by weightand particularly between about 62% and 67%. The remainder of thecomposition is advantageously water.

The above composition is mixed with nitric acid and water to form anetching bath containing, for example, between about 12% and 16% byweight of nitric acid, 0.6% and 1% of sulfated castor oil, 0.007% and0.05% by weight of alkyl aryl sulfonate, 1.4% and 1.8% by weight ofpetroleum solvent and the remainder water. Advantageously, theproportions of the above ingredients are respectively between 13% and14.5%; 0.7% and 0.9%; 0.02% and 0.03%; and 1.5% and 1.6% by weight.Excellent results have been achieved when the ingredients have been usedin approximately the proportions set forth in the following example:

Percent by volume 42 Baum nitric acid 13.8 Aromatic petroleum solvent(Aromatic content While solutions made according to the presentinvention can be used to good advantage in etching plates composed of avariety of metals, excellent results'have been achieved with zinc andmagnesium alloys. Examples of such alloys are as follows:

A. Zinc-base alloys: I

(1) 0 to 1.0% cadium; 0 to 0.025% iron; 0 to 0.05% magnesium; 0 to 0.2%nickel; and remainder zinc;

(2) 0 to 1.0% aluminum; 0 to 0.05 magnesium; and remainder zinc; and

(3) At least 90% zinc and the remainder, other metals.

B. Magnesium-base alloys:

' (1) 3% aluminum; 1% zinc; 0.2% manganese; and remainder magnesium; and

(2) At least magnesium and the remainder, other metals.

The invention will be described in greater detail with reference to thefollowing examples which are intended to be illustrative of theinvention and not restrictive thereof. In the examples, parts andpercentages are by weight.

Example I calculated as KOH), 0.025% dodecyl benzene sulfonic acid, andthe remainder water, was formulated and used to etch a zinc alloy platecontaining about 0.1% aluminum, 0.06% magnesium and less than about0.005% of other metals. The etching was conducted for about 20 minutesand produced a depth of etch of about 0.04 inch, a half-tone depth ofabout 0.006 inch in 10% 65 screen half-tones and a bowl depth of about0.015 inch. No undercutting of the images was observable upon inspectionof the plate with a 10X magnifying glass.

In contrast, when using an etching bath in which the sulfated castor oilwas omitted, severe undercutting occurred, yielding a plate completelyunsatisfactory for printing.

The use of an etching bath similar to the bath of the invention but inwhich the alkyl aryl sulfonate was tory for printing.

Example II The procedure of this example was the same as that of Example1, except that the sulfated castor oil mixture had an organicallycombined S content of about 8%, an acid value of about an alkalinity ofabout 2.4%. Also, 0.031% of dodecyl benzene sulfonic acid was employed.

The etched plates produced with the above bath exhibited the samesuperiority of etch shown by the plates produced with the bath of theinvention in Example I.

The above description and examples show that the present inventionprovides a novel etching composition and etching method. The etchingcomposition of the invention provides a greater flexibility in bathformulations and permits the use of a wider range of sulfated castoroils. Furthermore, the etched image so produced has a smoother shoulderangle, and undercutting is eliminated. Moreover, the speed of etching issignificantly faster.

It will be apparent that various modifications in the composition andmethod described may be made within the scope of the invention. notintended to be limited to'the specific formulations and procedures setforth in detail herein except a may be required by the following claims.

What is claimed is:

1. An additive for an etching composition consisting essentially ofbetween about and 40% by weight of a sulfated castor oil, between about0.3% and 2% by weight of an alkyl-benzene sulfonate having an alkylgroup containing between about 10 and 12 carbon atoms,

and between about 60% and 72% by weight of a pctroleum solvent.

2. An additive for an etching composition consisting essentially ofbetween about and by Weight of a sulfated castor oil, between about 0.9%and 1.2%

by weight of an alkyl-benzene sulfonate having an alkyl group containingbetween about 10 and 12 carbon atoms, and between about 62% and 67% byweight of a pctroleum solvent.

3. An additive for an etching composition according to claim 1 in whichthe sulfated castor oil contains between about 6% and 9% by Weight on adry basis of organically combined S0 and the solvent is an aromaticpetroleum solvent.

4. An additive for an etching composition according to claim 1 in whichthe aromatic content of the solvent is about 90% and the flash point isabout 150 F.

5. An additive for an etching composition according to claim 1 in whichthe alkyl-benzene sulfonate is sodium dodecyl benzene sulfonate.

6. An additive for an etching composition according to claim 1 in whichthe sulfated castor oil on a dry basis has an organically combined S0content between about 6% and 9% by weight, an acid value between about18% and 25% by weight calculated as oleic acid and an alkalinity betweenabout 2.2% and 3% by weight calculated as KOH.

7. An aqueous etching bath consisting essentially of between about 0.6%and 1% by Weight of a sulfated castor oil, between about 0.007% and0.05% by weight Therefore, the invention is of an alkyl-benzenesulfonate the alkyl group containing between about 10 and 12 carbonatoms, between about 1.4% and 1.8% by weight of a petroleum solvent,between about 12% and 16% by weight of nitric acid, and water.

8. An aqueous etching bath consisting essentially. of between about 0.7%and 0.9% by weight of a sulfated castor oil, between about 0.02% and0.03% by weight of an alkyl-benzene sulfonate having an alkyl groupcontaining between about 10 and 12 carbon atoms, between about 1.5% and1.6% by weight of a petroleum solvent, between about 13% and 14.5% byweight of nitric'acid, and water.

9. An aqueous etching bath according to claim 7 in which the sul'fatedcastor oil on a dry basis has anorganically combined S0 content betweenabout 6% and 9% by weight, an acid value of between about 18% and 25% byweight calculated as oleic acid, and an alkalinity of between about 2.2%and 3% by weight calculated as KOH.

10. An aqueous etching bath according to claim 7 in which thealkyl-benzene sulfonate has an alkyl group containing between about 10and 12 carbon atoms.

11. An aqueous etching bath according to claim 7 in which thealkyl-benzene sulfonate is sodium dodecyl benzene sulfonate.

12. A method of etching a metal plate having portions of its surface.covered with an acid resistant coat-.

sulfated castor oil, between about 0.007% and 0.05%

by weight of an alkyl-benzene sulfonate having an alkyl group containingbetween about 10 and 12 carbon atoms, between about 1.4% and 1.8% byweight of a petroleum solvent, between about 12% and 16% by weight ofnitric acid, and water.

13. A method of etching a metal plate having portions of its surfacecovered with an acid resistant coating to define a design whichcomprises applying to the surface of the plate an etching bathconsisting essentially of between about 0.7% and 0.9% by weight of asulfated castor oil, between about 0.02% and 0.03% by weight of analkyl-benzene sulfonate having an alkyl group containing between about10 and 12 carbon atoms, between about 1.5 and 1.6% by weight of apetroleum solvent, between about 13% and 14.5% by weight of nitric acid,and water.

14. A method of etchingaccording to claim 12 in which the sulfatedcastor oil on a dry basis ha an organically combined S0 content between.about 6% and 9% by weight, an acid value between about 18% and 25 byweight calculated as oleic acid, and an alkalinity of between about 2.2%and 3% by weight calculated as KOH. V

References Cited by the Examiner UNITED STATES PATENTS 2,828,194 3/1958Hopkins et al. 25279.2 2,979,387 4/1961 Easely et al. 252-79.4 3,074,8361/ 1963 Sherer et al. 156-18 SAMUEL H. BLECH, Primary Examiner.

ALBERT T. MEYERS, JULIUS GREENWALD, LEON D. ROSDOL, Examiners.

W. E. SCHULZ, Assistant Examiner.

1. AN ADDITIVE FOR AN ETCHING COMPOSITION CONSISTING ESSENTIALLY OFBETWEEN ABOUT 25% AND 40% BY WEIGHT OF A SULFATED CASTOR OIL, BETWEENABOUT 0.3% AND 2% BY WEIGHT OF AN ALKYL-BENZENE SULFONATE HAVING ANALKYL GROUP CONTAINING BETWEEN ABOUT 10 AND 12 CARBON ATOMS, AND BETWEENABOUT 60% AND 72% BY WEIGHT OF A PETROLEUM SOLVENT.